The Border War is a rivalry between the athletic programs of the University of Kansas and the University of Missouri. It has been officially named the Border Showdown since 2004, and promoted as the Hy-Vee Hoops Border Showdown for basketball games since 2021. The rivalry is more known for football and men's basketball, though it exists in all sports.

The Kansas Jayhawks and the Missouri Tigers began playing each other in 1891. From 1907 to 2012 both schools were in the same athletic conference and competed annually in all sports. Sports Illustrated described the rivalry as the oldest (Division I) rivalry west of the Mississippi River in 2011, but went dormant after Missouri departed the Big 12 Conference for the Southeastern Conference on July 1, 2012. Despite Missouri wanting to continue athletic competition, no further regular season games were scheduled between the two schools for several years.Dodds, Dennis. "Once Glorious Missouri-Kansas Rivalry Ends (For Now) Quietly". However, the two schools played an exhibition game in men's basketball on October 22, 2017, with Kansas defeating Missouri 93–87. Proceeds went to four different charities for Hurricane Harvey and Hurricane Maria relief funds. On October 21, 2019, the schools agreed to play six basketball games beginning in 2020, however, due to the COVID-19 pandemic, the renewal was postponed one season. Then, on May 2, the schools made an agreement for football games to be played in 2025, 2026, 2031, and 2032.

The rivalry has historic roots in the often violent relationship between the states of Kansas and Missouri, including guerrilla warfare between the states before and during the American Civil War.

Background Many believe the rivalry can trace its history to open violence involving anti-slavery and pro-slavery elements that took place in the Kansas Territory and the western frontier towns of Missouri throughout the 1850s. These incidents were attempts by some Missourians (then a slave state) to influence whether Kansas would enter the Union as a free or slave state. The era of political turbulence and violence has been termed Bleeding Kansas. When the Civil War began, the animosity that developed during the Kansas territorial period erupted in particularly vicious fighting. In the opening year of the war, six Missouri towns (the largest being Osceola) and large swaths of western Missouri were plundered and burned by various forces from Kansas generically termed jayhawkers. These attacks led to a retaliatory raid on Lawrence, Kansas two years later (Lawrence Massacre), which led to General Order No. 11 (1863), the forced depopulation of several western Missouri counties. The raid on Lawrence was led by William Quantrill, a Confederate guerrilla born in Ohio who had formed his bushwhacker group at the end of 1861. Quantrill had earlier been a resident of Lawrence, teaching school there until the school closed in 1860. Quantrill also attacked a nearby town of Olathe causing chaos during the civil war.

A recent analysis of the rivalry's history by a University of Kansas professor concludes that historical memories of the Civil War era were not introduced into the athletic rivalry until the 1970s, and the historical angle did not seep into the popular imagination until the 1990s. A rebuttal provided extensive evidence the rivalry "from its start, was influenced by animosity dating to the Border War". Evidence cited included a newspaper article on the 1891 game opening with a reference to the Border War, and a University of Missouri professor stating in 1910, "the annual football game ... is but a continuation of the border warfare of earlier times." Additionally, an article on the rivalry written by Kansas football coach A. R. Kennedy in 1917 stated, "no wonder the border warfare terms of 'Jayhawk' and 'Bushwhacker' were revived, for in many ways football is a worthy successor to war."

The mascots of the two universities were also derived from this time period. The University of Kansas, like many other universities, had no official mascot during the early years of its existence. The football team had used many different independent mascots, including a pig. In the three years preceding and the decades following the Civil War, the term "Jayhawker" was generally an epithet denoting "plundering marauder" both in the Missouri–Kansas region and nationally.Western Home Journal; Lawrence, KS; December 9, 1875; Page 3. "The term 'Jayhawker' is a rival term to 'Marauder'. It is of similar import, and now threatens to displace its old ally from the vocabulary of western phrases."John Russell Bartlett, Dictionary of Americanisms: A Glossary of Words and Phrases, Usually Regarded as Peculiar to the United States, Fourth Edition. Boston: Little, Brown, and Company. 1877. "Jayhawker: A cant (slang) name in the Western States for a lawless or other soldier not enlisted; a freebooting armed man; a guerilla."The New York Times; January 1, 1893. "... our own (American) term for a lawless band who fight less for a cause than the sake of booty, 'The Jayhawkers'...."Conrad, Howard L. Encyclopedia of the History of Missouri, Vol. III. The Southern History Company, New York, 1901. Page 422. "A name applied to a set of marauders and robbers in Kansas, who made the border counties of Missouri, the field of predatory raids during the slavery troubles of 1855–60. They were adherents of the Free State cause in Kansas, and acted on the assumption that the people of Missouri were their enemies, whom they had a perfect belligerent right to plunder at discretion."Daniel E. Sutherland. "Jayhawkers and Bushwackers". The Encyclopedia of Arkansas History and Culture. "Jayhawker" originated in Kansas. ... Kansans liked the tough image it conveyed during those bloody days of pre–Civil War violence, and they continued to use it once the war began. Missourians applied the name to Kansans, too, but negatively. They thought it fit the destructive raiders who plundered and destroyed their property before and during the war.... This usage was so widely known by the time of the war that Arkansans called any Kansas troops who entered the state jayhawkers.... Jayhawkers would always be linked to Kansas, but so notorious had the violence perpetrated by early Kansas raiders become that the nature of the deed, rather than any geographical place, came to define the name." However, after Charles Jenison christened the Seventh Kansas Volunteer Cavalry "The Independent Kansas Jayhawkers" in 1861, the term also began to be used as a term for any troops from Kansas, and eventually by Kansans as a term they proudly applied to themselves.The Allen County Courant (Iola, Kansas), May 23, 1868; Vol. 2, No. 19. "Origin of the Word Jayhawking In Application to the People of Kansas. Incidents in the early History of the Territory." By the late 1800s, it had become synonymous with native Kansans, much like Hoosiers in the state of Indiana. According to the University of Kansas, when KU football players first took the field in 1890, they were called the Jayhawkers. The University of Missouri also adopted a Civil War-related name. When the MU football team was first formed in 1890, at a mass meeting of students and interested citizens held to perfect the organization of the team, "Tigers" was unanimously selected as the team name.The Missouri Alumnus. "Why M. U. Athletes are Called 'Tigers'". Volume V, No. 11, pp. 189–190. March 2, 1917. During the Civil War, the "Tigers" were a "home guard" unit that protected Columbia from guerilla attack. The Tigers militia unit was commanded by James Rollins, upon whom the MU's board of curators later bestowed the title of "Pater Universitatis Missouriensis" (Father of the University of Missouri) in recognition of his "great efforts to promote the posterity, usefulness, and success" of the university.Smith, William Benjamin. James Sidney Rollins, Memoir. New York: De Vinne Press, 1891. Page 49. Ironically, they once protected Columbia from attack by a band led by "Bloody Bill" Anderson, who participated in the Burning of Lawrence along with Quantrill.http://www.columbiatribune.com/news/2011/sep/25/tigers-football-had-a-modest-beginning/?webapp#fontsize

Over time, even the coaches have gotten into the rivalry. Former Kansas football coach Don Fambrough, when referred to a physician across the state line in Kansas City, Missouri, for treatment, exclaimed "I'll die first!""Opinion: Border War never mattered more" MSNBC Not to be outdone, Missouri's former basketball coach Norm Stewart would traditionally have his players stay in Kansas City, Missouri, before playing at Kansas, going so far as to require the team bus to buy its gasoline at a Missouri filling station and reprimanding players who ate in Kansas, as he did not want to put any money into Kansas's economy.

The 2007 football season brought the origins of the rivalry between the two states back into the spotlight. A T-shirt created by a Missouri alumnus gained national attention with its reference to Quantrill's raid of 1863. The Missouri alumnus used the shirt to celebrate Missouri pro-slavery fighters burning the town of Lawrence, Kansas. The residents of Lawrence were largely Jayhawkers. – NCAAFB FanHouse The shirt depicted the burning of Lawrence in 1863 following the raid of William Quantrill and his Bushwhackers. The image of Lawrence burning was paired with the word "Scoreboard" and a Mizzou logo. On the back of the shirts, William Quantrill was quoted, saying "Our cause is just, our enemies many." Some Kansas fans interpreted these shirts as supporting slavery, and in recent years, the epithet "Slavers" has been employed by many KU fans to refer to anything related to Missouri. KU supporters returned fire with a shirt depicting abolitionist John Brown with the words, "Kansas: Keeping America Safe From Missouri Since 1854. Columbia Missourian, July 24, 2012

Name change In 2004 its name was officially changed from Border War to the Border Showdown. KU athletic director Lew Perkins stated, "We feel that in the aftermath of September 11, 2001, and the ensuing events around the world, it is inappropriate to use the term 'war' to describe intercollegiate athletics events.""'Border War' no more; KU-MU series retitled" LJWorld The name change was generally criticized by people on both sides. Players, students, alumni, and fans failed to adopt the new name, and even media outlets such as Sports Illustrated and NBC continued to refer to the rivalry as the Border War.

Basketball Kansas leads the all-time series, 177–95.

Notable games 1906–07 – Missouri began the basketball border showdown in Columbia against the Jayhawks with a 34–31 triumph, and the following day followed it up with a 34–12 beating. This left Missouri with a 2–0 all-time record against the inventor of basketball, and Kansas's first coach, James Naismith. 1909–1910 – Each of the basketball teams had players from the team's football squad (Tommy Johnson for Kansas, and Ted Hackney for Missouri). The players picked up where they left off from the gridiron, playing a rough and tumble style that, some stories say, caused James Naismith to exclaim, when viewing the second contest between the two, "Oh, my gracious! They are murdering my game!" Kansas won both meetings. 1922 – Kansas and Missouri split their conference games, tying for the Missouri valley title at 15–1. Although Missouri's committee on intercollegiate athletics challenged Kansas to a one-game playoff at a neutral site, Phog Allen refused to accept, leaving the decision to Kansas's athletic board and Chancellor, who declined. While no national champions were actually crowned until 1938 when the first national tournament was held, in 1936 Kansas was retroactively awarded a Helms Foundation National Championship. The title was again awarded to Kansas for the 1923 season.